Author Topic: Annoyed to find my new BB is part plastic  (Read 1717 times)

Annoyed to find my new BB is part plastic
« on: 05 August, 2018, 06:25:24 pm »
I'm not sure if this is the right board, so please move it if it's in the wrong place, anyway... I had to replace my Shimano cartridge BB (Square taper UN something, I can't think of the number). The worn out one was all metal, both the bit which houses the bearings and the piece which screws in the other side. When I got the new one I found that the piece for the other side had been changed to plastic. I couldn't just swap the old one over as they didn't quite fit. I think it's bad enough that the unit is sealed (although it seems like it is possible to overhaul it, I might try to refit the old one with new bearings), but to put plastic in means that it's life is limited to the plastic becoming brittle and aged. I also nearly cross threaded it the first time I tried to fit it, and also had no idea how tight I could do it up before I stripped the threads.

I know that it's very likely I'll wear the bearings out long before the plastic gives up, but the whole idea of selling something so flimsy and throwaway really annoyed me. I'll definitely switch to a different brand if I can track down something which is all metal. Has anyone else had a problem with this or am I just moaning about nothing?

rogerzilla

  • When n+1 gets out of hand
Re: Annoyed to find my new BB is part plastic
« Reply #1 on: 05 August, 2018, 06:34:34 pm »
Some of them (it seems random) have had plastic LH cups for years and years.  The most recent ones I've bought have been metal.  They all work fine.

Tange are always metal on both sides if you want a JIS alternative.  They go down to 103mm too.
Hard work sometimes pays off in the end, but laziness ALWAYS pays off NOW.

Cudzoziemiec

  • Ride adventurously and stop for a brew.
Re: Annoyed to find my new BB is part plastic
« Reply #2 on: 05 August, 2018, 06:35:26 pm »
I think this is not a design change but two different models.
Riding a concrete path through the nebulous and chaotic future.

Re: Annoyed to find my new BB is part plastic
« Reply #3 on: 05 August, 2018, 07:55:09 pm »
I'm not sure if this is the right board, so please move it if it's in the wrong place, anyway... I had to replace my Shimano cartridge BB (Square taper UN something, I can't think of the number). The worn out one was all metal, both the bit which houses the bearings and the piece which screws in the other side. When I got the new one I found that the piece for the other side had been changed to plastic. I couldn't just swap the old one over as they didn't quite fit. I think it's bad enough that the unit is sealed (although it seems like it is possible to overhaul it, I might try to refit the old one with new bearings), but to put plastic in means that it's life is limited to the plastic becoming brittle and aged. I also nearly cross threaded it the first time I tried to fit it, and also had no idea how tight I could do it up before I stripped the threads.

I know that it's very likely I'll wear the bearings out long before the plastic gives up, but the whole idea of selling something so flimsy and throwaway really annoyed me. I'll definitely switch to a different brand if I can track down something which is all metal. Has anyone else had a problem with this or am I just moaning about nothing?

Hi Tom. I am afraid the it is all in the name of Lightness,Cost effectiveness and more time cycling and less time faffing about crawling about the floor looking for the bearings that have escaped  ;D
I have been using cartridge bottom brackets for years and never had a failure as yet albeit I did receive a defective one that was replaced without question;it was so thight that the spindle would not revolve when turned by hand.

The did not want it back as it was fully sealed - BIN JOB.
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robgul

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Re: Annoyed to find my new BB is part plastic
« Reply #4 on: 05 August, 2018, 08:41:16 pm »
The LH cup barely does anything other than reducing the water and muck that might get into the BB shell and a minute amount of possible flexing so don't worry about it being plastic.

Rob

Re: Annoyed to find my new BB is part plastic
« Reply #5 on: 05 August, 2018, 09:15:56 pm »
Plastic, specified correctly, is a perfectly sound engineering material.

Re: Annoyed to find my new BB is part plastic
« Reply #6 on: 05 August, 2018, 10:12:18 pm »
the plastic cups seem to work quite well if they installed correctly. For their own mad reasons,  shimano have made it so that some of their BBs which come with a metal LH cup these days come with one that does not fit properly; it is way too loose. This tends to pass a lot of extra load through the RH threads on the BB shell, and I have seen several aluminium frames that have failed as a result.

cheers

Re: Annoyed to find my new BB is part plastic
« Reply #7 on: 06 August, 2018, 10:01:17 am »
There is a really good property of a plastic part; if you do happen to cross-thread it during fitting, it's the plastic threads that will get chewed up, not the metal ones. This will save you from wrecking the shell and some very expensive repair costs.

Re: Annoyed to find my new BB is part plastic
« Reply #8 on: 06 August, 2018, 11:03:10 am »
UN26 and UN54 are plastic cup, UN55 is alloy cup

fruitcake

  • some kind of fruitcake
Re: Annoyed to find my new BB is part plastic
« Reply #9 on: 06 August, 2018, 01:30:45 pm »
The only installation issue I've noticed is when the BB shell threads are dirty or slightly corroded. Where as a steel cup ina  steel frame will just plough through this kind of crud, the plastic one may lose part of its thread. Makes cleaning the shell more important.

I've only seen one plastic 'cup' that had failed and that was because the owner had tried to remove it without the proper tool, and chewed up the plastic teeth in the process. This was a on a frame he was hoping to sell. It occured to me afterwards that he could have removed it by cutting it into pieces in situ.

Re: Annoyed to find my new BB is part plastic
« Reply #10 on: 06 August, 2018, 01:44:00 pm »
Thanks for all the replies! I think partly it's just a feeling that metal is the 'proper' material for parts to be made of, even if plastic is perfectly good :) I also realised that it was lighter which has got to be a good thing. I'm sure I'll forget about it soon enough. The main thing is that my BB isn't clicking on each right hand pedal stroke anymore!

bludger

  • Randonneur and bargain hunter
Re: Annoyed to find my new BB is part plastic
« Reply #11 on: 06 August, 2018, 02:02:55 pm »
There are some great plastics out there in the world market such as zytel. https://en.wikipedia.org/wiki/Zytel

I'd quite happily give an all-plastic bike a go if it passed the relevant quality and safety benchmark tests!

Some Bristol University boffins gave it a crack 7 years ago https://www.bbc.co.uk/news/av/uk-12664422/bristol-engineers-invent-super-strong-nylon-bicycle
YACF touring/audax bargain basement:
https://bit.ly/2Xg8pRD



Ban cars.

Re: Annoyed to find my new BB is part plastic
« Reply #12 on: 06 August, 2018, 02:35:09 pm »
I'd quite happily give an all-plastic bike a go if it passed the relevant quality and safety benchmark tests!
You mean like these: https://road.cc/content/feature/211921-13-best-carbon-fibre-road-bikes-ps699-ps10000

<i>Marmite slave</i>

Chris N